This proposal is to design and build an easy-to-use, 3-D imaging system for cardiac catheterization by applying a novel algorithm to produce a live, 3-D reconstruction of the coronary artery tree. The proposed system requires three or four projections and shows complex vessel cross-section in greater detail. It provides an efficient and more accurate method for guiding catheterization and evaluating coronary vessel pathoanatomy than the 2-D method. With 2-D, the observer derives an estimate of the narrowing of vessel diameter by looking at, and averaging, two 2-D projections taken at right angles to each other. The limitations of the 2-D method are: First, a significant error of estimating lumen size may occur when an atherosclerotic plaque is not perfectly round, is located eccentrically within the lumen, or has an irregular shape. Second, foreshortened views of some parts of vessels require repositioning of the x-ray camera system. Repositioning distracts the observer, prolongs the procedure, and increases the risks to the patient. Third, repositioning requires repeated injection of the contrast dye, stressing the patient physiologically. The new method has the potential to replace the visual interpretation of 2-D coronary arteriograms for guiding cardiac catheterization and would supercede reliance on the 2-D method, which has been the 'gold-standard' for pathoanatomy of coronary heart disease. The goal is to simplify the catheterization procedure, make it safer, and reduce its cost.